So, I think it's largely safe to presume that the core of Western musical theory developed almost entirely within Europe -- Greece in its very early history, mainly Italy and also the Franco-Flemish regions during the middle ages and Renaissance, and perhaps a little after that elsewhere.

There are however notable exceptions. Spain's role in the development of classical music cannot be understated, I think. While we may not remember many famous early Spanish composers, I have heard that they were instrumental (no pun intended) in developing various forms of classical composition, perhaps bringing some in from the Middle-Eastern and North Africans musical traditions.

So here are a few of my proposals to start us off:

Some compositional forms popular in the Renaissance and Baroque, e.g. sarabande and passacaglia, are suggested to have originated in the Middle East/Arabia, in some loose stylistic sense.

The horse-travelling nomads of Central Asia are rumoured to have invented and indeed introduced the first bowed string instruments to Europe, which the Italians adopted and improved by way of the Byzantines. (Early examples of harps and lyres were of course found in Ancient Greece and indeed ancient Celtic regions for the former.)

Does anyone else have some suggestions, tentative or well-supported, to share?

I think your question is a bit too broad. You may want to consider asking a different question that is more specific, or splitting this into multiple questions (like how did specific culture affect Western classical music during specific time period?) Just a thought.
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StephenNov 16 '11 at 1:38

@Stephen: Not really. I want to see what ones are out there! If I'm not yet aware enough to ask about specific, then I simply cannot.
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NoldorinNov 17 '11 at 1:05

yes really. otherwise conflicting answers result. not good. suggestions for how to split q: 2nd paragraph of post mentions 'Spain' but title mentions 'external culture' -> ask about specific country / geography & contextualize /w something like 'when was Spanish music culture considered external to European music culture?' First paragraph is about theory. split that into questions about specific theoretical aspects e.g. rhythmic or pitch structures. '1.' is about dances and '2.' is about instruments -> split those into questions about specific practices / artifacts etc. to get @ diff times.
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user1217Nov 17 '11 at 13:38

@user1217: No need for the hostility. You're not understanding my questions even. Also, those two forms quickly developed into styles of piece (often keyboard music) if you know your music history. The question is quite clear as I see it.
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NoldorinNov 17 '11 at 15:33

3 Answers
3

1) American jazz has had a huge influence on 20th-century Western classical music. American jazz originated outside of 20th-century Western classical music. But now its harmonic and rhythmic vocabulary have permanently influenced Western classical music.

2) Minimalism, a la Steve Reich and Philip Glass, came from a conscious attempt to incorporate polyrhythms and repetitive rhythmic and melodic phrases into Western classical music. The concepts behind these polyrhythms and phrases come from studying traditional African drumming. So sub-Saharan African music now influences modern Western classical music.

In my opinion the overriding characteristic of post-modern Western classical music is its emphasis on percussion instruments, on the one hand, and rhythmic complexity in general on the other.

3) Film and the motion picture industry has tremendously re-shaped Western classical music. This started in the 1920s with composers being commissioned to write accompaniment music for live orchestras to play in sync with silent movies. Then when motion picture technology incorporated sound recording, filmmakers the world over enlisted composers to compose and record soundtracks. Writing music to motion pictures has changed compositional techniques significantly, as a practical consideration.

4) Bartok and Stravinsky, among others, championed the use of frequently-changing odd-time signatures, and the impetus for this seems to be various Eastern-European and Middle-Eastern folk music traditions--although 20th century composers took these compositional devices much further. Frequently-changing odd-time signatures are now used in all kinds of classical music, not the least of which are film scores, where phrasing, meters, and tempos shift constantly so the music can follow and accentuate the action on the screen.

5) Charles Ives, Aaron Copland and others incorporated Appalacian folk music and other folk music from the United States of America. This did not have as heavy an implication as what others were doing with jazz, but it is an influence nonetheless.

6) I must also mention Caribbean and South American popular music, not the least of which comes from Brazil. Along with this comes the fertile cross-over of New World classical guitar music (Leo Brouwer in Cuba, etc.)

There's some precedent for (4) in Chopin, Liszt, Debussy, and even Brahms. Etudes in particular are prone to time changes. Perhaps the 20th-c. composers were merely developing a previously-tapped source.
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luser droogNov 21 '11 at 8:29